The field of art to which this invention pertains is the preparation and treating of a fluid catalytic cracking (FCC) feed and the production of an ultra low sulfur diesel stream with high quality and high cetane index from a hydrocarbonaceous feedstock of straight run and/or cracked stock origin. Hydrotreating processes have been used by petroleum refiners to produce more valuable hydrocarbonaceous streams such as naphtha, gasoline, kerosene and diesel, for example, having lower concentrations of sulfur and nitrogen. Feedstocks most often subjected to hydrotreating are normally liquid hydrocarbonaceous streams such as naphtha, kerosene, diesel, gas oil, vacuum gas oil (VGO), and reduced crude, for example. Traditionally, the hydrotreating severity is selected to produce an improvement sufficient to produce a marketable product. Over the years, it has been recognized that due to environmental concerns and newly enacted rules and regulations, saleable products must meet lower and lower limits on contaminants such as sulfur and nitrogen. Recently new regulations are being proposed in the United States and Europe which basically require the complete removal of sulfur from liquid hydrocarbons which are used as transportation fuels such as gasoline and diesel.
Hydrotreating is generally accomplished by contacting the hydrocarbonaceous feedstock in a hydrotreating reaction vessel or zone with a suitable hydrotreating catalyst under conditions of elevated temperature and pressure in the presence of hydrogen to yield a product containing desired maximum limits of sulfur. The operating conditions and the hydrotreating catalysts within the hydrotreating reactor influence the quality of the hydrotreated products.
Although a wide variety of process flow schemes, operating conditions and catalysts have been used in commercial hydrotreating activities, there is always a demand for new hydrotreating methods which provide lower costs and required product quality and specifications. With the mandated low sulfur transportation fuels, the process of the present invention greatly improves the plot space requirements and the economic benefits of simultaneously producing hydrotreated cracking feedstocks and low sulfur diesel stocks in one unit. The hydrotreated cracking feedstock will allow the production of low sulfur gasoline to be produced from a downstream FCC unit.
U.S. Pat. No. 3,540,999 (Jacobs) discloses a process for converting heavier hydrocarbonaceous material into jet fuel kerosene and gasoline fractions. The simultaneous production of both jet fuel and gasoline fractions, in maximum quantities, is afforded through the utilization of a modified xe2x80x9cseries-flowxe2x80x9d system. A two-stage process in which the jet fuel kerosene fraction is produced in the first stage with the gasoline fraction being produced in the second stage.
U.S. Pat. No. 5,114,562 (Haun et al) discloses a process wherein middle distillate petroleum streams are hydrotreated to produce a low sulfur and low aromatic product in two reaction zones in series. The effluent of the first reaction zone is purged of hydrogen sulfide by hydrogen stripping and then reheated by indirect heat exchange. The second reaction zone employs a sulfur-sensitive noble metal hydrogenation catalyst.
The present invention is an integrated hydrotreating process which combines two very different functions in one unit: (1) treating VGO boiling range material to prepare feed for the FCC and (2) treating low quality straight run or cracked diesel boiling range material to produce an ultra low sulfur diesel stream of high quality and high cetane index. A high boiling VGO feedstock is firstly hydrotreated to reduce the concentration of sulfur such that further cracking of the VGO material in the FCC unit will produce gasoline which would meet low sulfur specifications. The first hydrotreating zone is required to operate at a severity sufficient to reduce the sulfur content of gasoline which is subsequently produced. The resulting hydrocarbonaceous compounds boiling in the diesel range produced from the severe treating of the VGO material must be further hydrotreated to meet the new ultra low sulfur diesel specifications ( less than 10 PPM). The effluent from the first hydrotreating zone is introduced into a high pressure stripper preferably maintained at a temperature from about 149xc2x0 to 454xc2x0 C. (300xc2x0 to 850xc2x0 F.) to produce a gaseous hydrocarbonaceous stream comprising hydrogen and diesel boiling range hydrocarbons, and a liquid stream comprising hydrocarbons boiling above the diesel boiling range. A second hydrotreating zone is utilized to desulferize the previously vaporized diesel range hydrocarbons produced in the stripper which is economically achieved by the integration of the second hydrotreating zone with the first hydrotreating zone. Feed to the second hydrotreating zone will preferably include cracked and/or straight run diesel from various external sources and diesel produced in the first hydrotreating zone.
In accordance with one embodiment, the present invention relates to an integrated hydrotreating process for the production of a low sulfur diesel stream which process comprises: (a) passing a first hydrocarbonaceous feedstock and hydrogen to a first denitrification and desulfurization reaction zone operated at reaction zone conditions including a temperature from about 204xc2x0 to 482xc2x0 C. (400xc2x0 to 900xc2x0 F.) and a pressure from about 3.6 to 17.3 MPa (500 to 2500 psig) with a catalyst and recovering a denitrification and desulfurization reaction zone effluent therefrom; (b) passing the denitrification and desulfurization reaction zone effluent to a high pressure stripper maintained at a temperature from about 149xc2x0 to 454xc2x0 C. (300xc2x0 to 850xc2x0 F.) to produce a first vapor stream and a first liquid stream; (c) passing at least a portion of the first vapor stream and a second feedstock comprising diesel boiling range hydrocarbons to a second denitrification and desulfurization reaction zone to produce a second liquid stream comprising reduced sulfur content, diesel boiling range hydrocarbons and a hydrogen-rich gaseous stream containing hydrogen sulfide; (d) passing the hydrogen-rich gaseous stream containing hydrogen sulfide to an acid gas scrubbing zone to produce a hydrogen-rich gaseous stream having a reduced concentration of hydrogen sulfide; and (e) passing at least a portion of the hydrogen-rich gaseous stream having a reduced concentration of hydrogen sulfide to the high pressure stripper and the first denitrification and desulfurization reaction zone.
In accordance with another embodiment, the present invention relates to an integrated hydrotreating process for the treating of FCC feed to achieve low sulfur specifications in FCC gasoline and the production of an ultra low sulfur diesel stream which process comprises: (a) passing a first hydrocarbonaceous feedstock and hydrogen to a first denitrification and desulfurization reaction zone operated at reaction zone conditions including a temperature from about 204xc2x0 to 482xc2x0 C. (400xc2x0 to 900xc2x0 F.) and a pressure from about 3.6 to 17.3 MPa (500 to 2500 psig) with a catalyst and recovering a denitrification and desulfurization reaction zone effluent therefrom; (b) passing the denitrification and desulfurization reaction zone effluent to a high pressure stripper maintained at a temperature from about 149xc2x0 to 454xc2x0 C. (300xc2x0 to 850xc2x0 F.) to produce a first vapor stream and a first liquid stream; (c) passing at least a portion of the first vapor stream and a second feedstock comprising diesel boiling range hydrocarbons to a second denitrification and desulfurization reaction zone to produce a second liquid stream comprising reduced sulfur content, diesel boiling range hydrocarbons and a hydrogen-rich gaseous stream containing hydrogen sulfide; (d) passing the hydrogen-rich gaseous stream containing hydrogen sulfide to an acid gas scrubbing zone to produce a hydrogen-rich gaseous stream having a reduced concentration of hydrogen sulfide; and (e) passing at least a portion of the hydrogen-rich gaseous stream having a reduced concentration of hydrogen sulfide to the high pressure stripper and the first denitrification and desulfurization reaction zone.
Other embodiments of the present invention encompass further details such as types and descriptions of feedstocks, hydrotreating catalysts and preferred operating conditions including temperatures and pressures, all of which are hereinafter disclosed in the following discussion of each of these facets of the invention.